When using an insta-warp to another screen, the dark room screen flag carries over from the previous screen to the next. Example: If you're on a screen with a 'dark room' screen flag and you insta-warp to a screen that is not a dark room, it will use the dark room flag.
This works from light to dark and dark to light rooms and has been happening for a long time.
Link75 wrote:Example: If you're on a screen with a 'dark room' screen flag and you insta-warp to a screen that is not a dark room, it will use the dark room flag.
Have you checked the "Full Screen Warp" in the Screen Flags? (This gets every screen feature from the screen you are warping from and applies to the screen you entered) If so, not a bug.
If this still occurs with "Full Screen Warp" screen flag unchecked on the screen you are warping from, then it is a bug. Reply your decison.
So that's what full screen warp does. Awesome.
But still, the bug happens whether the "Full Screen Warp" screen flag is checked or not on either or both screens.
Okay, alright.
The developers will take care of this. The text in bold in post #2 notes that this bug is verified. 
Dark room carrys over while using Insta-Warp.
zcAmazing wrote:Have you checked the "Full Screen Warp" in the Screen Flags? (This gets every screen feature from the screen you are warping from and applies to the screen you entered)
That's not entirely true. Sprites - weapons, enemies, and items - are copied, as are some miscellaneous parts of the current room state such as sound effects playing, whether or not Link is using the clock, any heart rings on screen, etc. Screen flags, including the dark flag, are not copied.
In any case, insta-warps should now respect the destination's darkness flag.
I reported this back in the b16